1. Field of the Invention
This invention relates to a low voltage protective circuit breaker with an actuating lever that can be moved by an operating handle and is connected by means of a drive spring and two toggle levers to a control shaft on which movable contacts for the circuit breaker are mounted. In particular, the invention relates to a locking lever mounted on the control shaft to prevent moving the handle into its "off" position if the movable contact is blocked in its "on" position so that it remains conductively engaged with the fixed contact.
2. The Prior Art
A protective circuit breaker generally similar to the type described herein is shown in DE-OS No. 25 08 220 in which a locking lever is permanently connected to a control shaft and cooperates with a hinged stop in such a manner that the drive lever and, thereby, the handle mounted on the drive lever, are prevented from being transferred into their "off" position whenever the movable contact is blocked in its "on" position, as, for instance, by being welded to the fixed contact. If, on the other hand, the contacts are not welded together and a normal interruption occurs, the resulting rotation of the control shaft and the corresponding rotation of the locking lever lifts a stop to release the drive lever. In both instances, the latching of the switching mechanism is first released by a release member connected to the drive lever.
Another known device shown in U.S. Pat. No. 4,165,453 for blocking the driving lever if the contacts are blocked comprises a two-armed locking lever supported on the toggle joint of the toggle levers so that one of the arms fits within the turns of a helical drive spring for the toggle levers, while the other lever arm cooperates with the joint pin that connects the toggle levers to the carrier of the movable contact. When that circuit breaker is switched off by hand, the toggle levers are always snapped through in the "off" direction before the engagement direction of the drive spring reaches dead center. Normally, the movable contacts would then be opened completely, but if the movable contacts were blocked so that they could not disengage from the fixed contacts, the driver lever could no longer be pivoted further in the "off" direction because of locking of one lever arm against the movable contact remaining in the "on" position.